Metal cans are known in many embodiments. It is an object of the invention to shape a metal can, consisting substantially for instance of tin or aluminium which may or may not be provided with coatings consisting of lacquer, printing ink or the like, such that a desired form is obtained, wherein the cross-sectional form varies with the axial position.
It has been found in experiments that it is not possible to obtain desired body forms by only applying substantially radial forces to a can. Due to the stresses which occur the shaping process is very difficult to control and there is the danger of the body collapsing.
In respect of the above the invention provides a method for shaping a metal can comprising a substantially cylindrical body and a bottom such that the body acquires a cross-sectional form varying with the axial position, which method comprises the steps of:
(1) providing said can;
(2) exerting substantially radial forces on the body in the direction of the desired shaping; and
(3) exerting a substantially axial force on the body simultaneously with step (2).
Surprisingly, it has been found that by simultaneously exerting the forces acting in radial direction and exerting axial forces, the ability to shape the metal is improved considerably, whereby desired can shapes can be realized which correspond to comparatively high percentages of deformation.
With respect to the radial forces it is noted that in order to obtain a locally smaller diameter the radial forces must be exerted inwardly. When such a force is applied the can has a natural tendency to elongate. The axial auxiliary force in accordance with step (3) can be applied to the outside (tensile force) as well as to the inside (pressure force). It is also possible to start with a relatively small can which is subjected to locally outward directed radial forces. The can hereby has a natural tendency to become shorter. Also in this case the axial auxiliary force can be directed to the outside as well as to the inside.
In order to exert the said radial forces use can be made of mechanical means such as segmented pressure rings with variable diameter or a rubber press or pressure medium, for instance gas or liquid under pressure.
In order to exert radial pressure forces use can be made of simple pressing punches. To exert axial tensile forces a pressure force can be exerted on the bottom via the mouth of the can in combination with a tensile force which is applied by an annular claw on the edge zone of the mouth opening.
Particularly in the case where the desired final shape of a can displays a specific profiling, for instance a plurality of recesses, ribs, flat facets or the like, the method according to the invention can be performed such that the radial forces press a can body toward and against a shaping wall, which wall has a shape corresponding with the desired final shape of the can body.